Hydraulic thermostatic system with slave piston assembly



Sept. 27, 1966 P. R. STAPLES 3,

HYDRAULIC THERMQSTATIG SYSTEM WITH SLAVE PISTON ASSEMBLY Filed Dec. 7, 1964 W fi /fi AA I5 23 SN I 33,.- l: f' Ge 2 INVENTOR. PAUL R.- STAPLES WXM H 5 TTORNEY United States Patent 3,275,236 HYDRAULIC THERMOSTATIC SYSTEM WITH SLAVE PISTON ASSEMBLY Paul R. Staples, Louisville, Ky., assignor to General Electric Company, a corporation of New York Filed Dec. 7, 1964, Ser. No. 416,503 5 Claims. (Cl. 236 15) The present invention relates to a hydraulic thermostatic control system that is capable of operating through a wide temperature range, and particularly a high'temperature domestic oven supplied with such a thermostatic control system.

Hydraulic thermostats have been widely used as oven temperature controls for many years. They usually comprise a temperature sensing bulb located within the oven cavity and formed on one end of a capillary tube, while the opposite end of the capillary tube is joined to a bellows or diaphragm that acts against a circuit switch contact means Within the thermostat housing. This general type of oven thermostat is disclosed in the patent to W, I. Ettinger No. 2,260,014 dated October 21, 1941. A suitable thermally-responsive fluid for such a system is phenyl diphenyl chloride, but this fluid will not withstand a temperature much above 600 F. before it starts to chemically decompose and lose its important properties.

Normal cooking temperatures range from about 150 F. to 550 F., and a hydraulic oven thermostat is at the present time the best available choice of a controlling means for governing the temperature heating means. In recent times, a high temperature self-cleaning oven design has been introduced wherein the oven temperature "reaches a heat cleaning temperature range somewhere between about 750 F. and 950 F. for degrading and removing the food soil and grease spatter that accumulates on the walls of the oven cavity. Such a self-cleaning oven is described and claimed in the recent patent of Bohdan Hurko No. 3,121,158 of February 11, 1964.-

This high temperature oven has required the substitution of an electric thermostatic control system for the standard hydraulic oven thermostat used heretofore. The present invention relates to an acceptable design of temperature sensor for a hydraulic thermostatic control system for use at temperatures a great deal above 600 F. and as high as 1000 F., wherein the standard thermostat fluid may be utilized.

The principal object of the present invention is to provide a hydraulic thermostatic control system with a temperature sensor having a direct expansion sensing tube exposed to the temperature to be controlled and a remotedriven tube where variations in the length of the sensing tube are reflected as variations in the length of the driven tube, there being a transducer cooperating with the driven tube for converting variations in the length of the driven tube to variations in the hydraulic pressure of the thermostatic system.

A further object of the present invention is to provide a temperature sensor of the class described with a fulcrum rod and rocker arm assembly for transmitting the motion in the sensing rod to the driven tube.

A further object of the present invention is to provide a hydraulic thermostatic control system with a temperature sensor having an open framework comprising a sensing tube, a fulcrum rod and a driven t-ube, there being levers connecting the adjacent ends of the tubes and rod, and a hydraulic slave piston assembly interposed in the driven tube to convert variations in the length of the driven tube to variations in hydraulic pressure of the thermostatic system.

A further object of the present invention is to provide 3,275,236 Patented Sept. 27, 1966 a thermostatic control system of the class described with a temperature sensor having a sensing tube, a fulcrum tube and a driven tube where the driven tube includes a slave piston that varies the pressure of the thermostat fluid as a function of the expansion and contraction of the sensor tube due to temperature changes, while the fulcrum tube and driven tube are ambient temperature compensated so that the net effect is that only the length of the sensor tube is monitored by the slave piston.

A still further object of the present invention is to provide a temperature sensor of the class described where the fulcrum tube and driven tube have different thermal time constants, such as the fulcrum tube having a greater thermal time constant than the driven element so as to provide anticipation and reduce the temperature amplitude as well as improve the sensitivity of thev system.

The present invention, in accordance with one form thereof, is embodied in a hydraulic thermostatic control system having a temperature sensor and an adjustable thermostat or responder that are joined together by a fluid-filled capillary tube. The temperature sensor is an open framework having a group of three substantially parallel tubes namely, a sensing tube, a fulcrum tube, and a driven tube where the adjacent ends of the tubes are connected together by a rocker arm. The sensing tube is to be exposed to the particular temperature that is tn be controlled, while both the fulcrum tube and the driven tube are located remotely in an ambient condition of relatively low temperature. The driven tube includes a transducer or slave piston assembly that is capable of functioning due to variations in the length of the driven tube to supply power to the thermostat fluid so as to change the pressure thereof, all of this as a function of variations in the length of the sensing tube which depends upon changes of temperature within the area to be controlled. A feature of importance is the fact that both the fulcrum tube and the driven tube are ambient temperature compensated so that only the length of the sensor tube is monitored by the slave piston assembly.

My invention will be better understood from the following description taken in conjunction with the accompanying drawing and its scope will be pointed out in the appending claims.

FIGURE 1 is a fragmentary left side elevatioual view of the upper portion of a free-standing electric range having an oven that is supplied with the hydraulic thermostatic control system of the present invention, there being parts broken away to show the temperature sensor protruding into the oven cavity, while the adjustable thermostat that is associated with the sensor is located in the control panel of the range.

FIGURE 2 is a fragmentary plan view of the temperature sensor at the back wall of the oven taken on the line 22 of FIGURE 1.

Turning now to a consideration of the drawing and in particular to FIGURE 1, there is shown for illustrative purposes the top portion of a free-standing electric range 10 having a top cooking surface or cooktop 11 with a plurality of surface heating elements 12, an oven cavity 13 located beneath the cooktop 11 and formed by a box-like oven liner 14 and a front-opening access door 15. The oven liner 14 is surrounded by a thermal insulating material 17 such as fiberglass or the like so as to retain as much of the heat generated within the oven cavity and be able to operate the oven at higher efficiency. A back panel or insulation guard 18 covers the back portion of the oven at a plane recessed from a back Wall 19 of the range so as to provide a wiring chamber 20 at the back of the oven as is conventional in this art.

The surface heating elements 12 are controlled by suitable selector switches 22 shown built into the side arms of the cooktop 11. The standard heating means of an electric oven comprises an upper broil unit 22 adjacent the top wall of the oven liner and a lower bake element (not shown) adjacent the bottom wall of the oven liner. Such heating elements are usually metal sheathed resistance heaters made of substantially the same construction as the surface heating elements 12. Overhead of the broil element 22 is a downturned reflector pan 23 that is used to shield the radiant energy from the broil unit 22 away from the top wall of the oven liner and reflect it toward the food placed in the oven cavity so as not to waste heat energy out through the top of the oven. The bake and broil oven heating elements are usually controlled by electrical components located on a control panel or backsplash 27 of the range shown as being located above and along the back edge of the cooktop 11. Such a control panel would include an oven selector switch, oven thermostat 28, perhaps an oven clock-timer as well as a meat thermometer control.

The above-described range construction is more or less conventional in this art, and it was presented in order to provide background information for facilitating the understanding of the hydraulic oven thermostatic control system embodying the present invention. Such a control system includes an adjustable thermostat 28, a temperature sensor 29, and a capillary tube connecting the sensor with the thermostat. Both the adjustable thermostat 28 and the capillary tube 30 may be of standard construction that is available on the market today from many sources. The primary area of novelty this invention lies in the temperature sensor 29 which may be best explained with relation to FIGURE 2. The sensor 29 is in the form of an open framework, and more specifical- 1y a rectangular frame, where one longitudinal side of the frame is a temperature sensing tube 32 and the opposite side is a driven tube 33. Then to close the frame, the opposite two sides of the frame are represented by rocker arms 34 and 35 which are each made integral with the adjacent ends of the sensing tube 32 and driven tube 33. Then at substantially the longitudinal center of the sensor frame is a fulcrum rod or tube 36 that is generally parallel with the sensing and driven tubes 33 and 33 respectively, and likewise made integral with the rocker arms 34 and 35 at the end of the rod, as at 37 and 38, respectively.

It has been deemed important to locate the sensing tube 32 within the oven cavity 13, while shielding the fulcrum rod 36 and driven tube 33 from the oven temperature by locating them Within the wiring chamber 20 in an ambient condition having relatively low temperatures. The purpose of shielding both the fulcrum rod 36 and the driven tube 33 from the oven temperature and locating them in the same ambient conditions is to render them ambient temperature compensated so that the net effect is that only the sensor tube length is monitored by the driven tube. Upon an increase in ambient temperature an outward expansion of the fulcrum rod 36 cancels the inward expansion of the two portions of the driven tube so that the net effect at the slave piston is zero. This objective is accomplished by forming a horizontal slotted opening 40 through the back wall of the oven liner 14 as well as through the fiberglass insulation 17 and the insulation guard 18. Thus, it is possible to insert the sensor 29 through the opening 40 until the sensing tube 32 protrudes into the oven cavity 13, while the fulcrum rod 36 stops short of the insulation guard 18 and remains with the driven tube 33 in the wiring chamber 20. An inner face plate 42 is adapted to close a large portion of the slotted opening 40 in the back wall of the oven liner by being inserted behind the sensing tube 32'. This plate has a pair of horizontally spaced vertical slots 43 to straddle the rocker arms 34 and 35 so the face plate is capable of assuming the position shown in FIGURE 1, and is held in place by suitable fastening means 44. The temperature sensor 29 must also be supported from the oven walls, and this is accomplised by a pair of bracket members 46 that are each brazed or otherwise made integral with one of the rocker arms adjacent the point of connection with the fulcrum rod 36. Each bracket 46 is in turn fastened to the insulation 'guard 18 as by means of the fastening screw 47.

The term transducer was used previously and it may be defined as a device that is actuated by power from one system and supplies power in the same or any other form to a second system. Such a transducer is identified as element 49, and it is disposed in the driven tube 33 as is best seen in FIGURE 2. The transducer 49 is made to be sensitive to changes in the length of the driven tube 33 whereby these changes are reflected as changes in the hydraulic pressure of the fluid filling the transducer 49, capillary tube 30 as well as the bellows of the adjustable thermostat 28. To be more specific, the transducer 49 is a hydraulic slave piston assembly having a cylinder 50 and piston 51. The cylinder 50 is connected at its closed end to one half of the driven tube 33. The piston 51 has a slender piston rod 52 which extends through a suitable opening in the cylinder 50 for connection to the remaining half of the driven tube 33.

In a preferred embodiment of the present invention the sensing tube 32 is formed of thin stainless steel tubing or the like so as to have a low thermal mass as well as rigidity in the lengthwise direction so that it will not tend to buckle under compressive loads. Nor will the sensing tube tend to bend if it were nudged by a cooking utensil being shifted around within the oven. In a similar mannor, the driven tube 33 is also a thin tubular member. However, the fulcrum rod 36 should be of extra strength, hence in the illustrated embodiment it has been made of solid bar stock. The same is true of the rocker arms 34 and 35. Hence, it will be recognized that changes in the temperature within the oven cavity 13 will tend to expand or contract the length of the sensing tube 32. The rocker arms 34 and 35 are adapted to pivot about the end of the fulcrum rod 36 in a direction depending upon whether the length of the sensing tube 32 is increasing or decreasing. The action here is to have the rocker arms 34 and 35 transmit forces from the sensing tube 32 to the driven tube 33 so that the driven tube will act in an inverse manner with relation to the sensing tube 32. When the oven temperature is increasing, the sensing tube 32 is expanding in length while the driven tube 33 is compressed by the rocker arms 34 and 35 and is shortened to increase the pressure of the thermostat fluid.

Since the fulcrum rod 36 is of bar stock while the driven tube 33 is of tubular form, they will have different thermal time constants due to the greater thermal mass of the fulcrum rod. Thus it will be appreciated that the driven tube 33 will change its length due to thermal expansion or contraction before the fulcrum rod when these two elements are exposed to the same ambient change. Hence, this characteristic may be employed to provide anticipation and prevent oven temperature overshoot-0n the first temperature cycle as well as reduce the temperature amplitude and improve the sensitivity of the thermostatic system. Of course, if this feature of anticipation were not found necessary it could be avoided by substituting a tube for the fulcrum rod 36 to obtain uniform thermal time constants.

Modifications of this invention will occur to those skilled in this art, therefore, it is to be understood that this invention is not limited to the particular embodiments disclosed, but that it is intended to cover all modifications which are within the true spirit and scope of this invention as claimed.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A hydraulic thermostatic system for controlling the heating means of a domestic oven comprising a temperature sensor and a hydraulic temperature responder that are joined together by a fluid-filled capillary tube, the sensor comprising a rectangular frame with a sensing tube a low thermal mass forming one side, a driven tube forming the opposite side, and where the two remaining sides are rocker arms connecting the sensing tube with the driven tube, and a fulcrum rod adjacent the center of the frame and integral at each end with the adjacent rocker arm. and a transducer cooperating with the driven tube and connected to the capillary tube so as to convert variations in the length of the driven tube to variations in the fluid pressure in the capillary tube, the sensing tube being adapted to be positioned within an oven cavity While both the fulcrum rod and the driven tube are adapted to be shielded from the oven temperature and located in the same ambient conditions to render them ambient temperature compensated so that the net effect is that only the sensor tube length is monitored by the driven tube.

2. A hydraulic thermostatic system having a temperature sensor and a hydraulic responder that are joined together by a fluid-filled capillary tube; the invention comprising the temperature sensor in the form of a rectangular frame having a temperature sensing tube of low thermal mass at one side, a driven tube at the opposite side, and a pair of rocker arms at the remaining sides connecting the sensing and driven tubes, and a fulcrum rod adjacent the center of the frame and bridged between the two rocker arms, the driven tube including a transducer connected to the capillary tube for converting variations in the length of the driven tube to variations in hydraulic pressure in the capillary tube, the sensing tube being adapted to be positioned within an oven cavity while both the fulcrum rod and the driven tube are adapted tobe shielded from the oven temperature and located in the same ambient conditions to render them ambient temperature compensated so that the net effect is that only the sensor tube length is monitored by the driven tube.

3. A domestic oven having walls defining an oven cooking cavity, one wall of the cavity including a door for gaining access thereto, heating means for the cavity for applying heat for cooking foods placed therein; the invention comprising a hydraulic thermostatic control system for the oven heating means having a temperature sensor associated with the oven cavity, a temperature responder at a remote point from the oven cavity, and a fluid-filled capillary tube connecting the sensor with the responder, the sensor being in the form of a rectangular frame having a temperature sensing tube of low thermal mass at one side, a driven tube at its opposite side, and a pair of rocker arms forming the two remaining sides, and a fulcrum tube braced between the two rocker arms and lying substantially in the center between the sensing tube and the driven tube, a transducer included in the driven tube and connected to the capillary tube for converting variations in hydraulic pressure in the capillary tube, the said sensing tube being located within the oven cavity, while both the fulcrum tube and the driven tube are located outside of the oven cavity and shielded therefrom while being exposed to the same ambient temperature conditions to render them ambient temperature compensated, the length of the sensing tube being sensitive to changes in the oven temperature, whereby variations in the length of the sensing tube will be transmitted by the rocker arms to the driven tube for changing the length thereof.

4. A domestic oven having walls defining an oven cooking cavity, one wall of the cavity including a door for gaining access thereto, heating means for the cavity for supplying heat for cooking foods placed therein, a hydraulic thermostat control system for governing the oven heating means, control system including a temperature sensor and an adjustable thermostat, and a fluid-filled capillary tube connecting the sensor to the thermostat, the sensor being in the form of an open framework having three spaced substantantially parallel rods, a temperature sensing rod, a central fulcrum rod, and a driven rod, the adjacent ends of the rods being joined together by a lever member that is integral therewith, the sensing rod being positioned within the oven cavity, while the lever members extend through a wall of the oven cavity to dispose both the fulcrum rod and driven rod outside of the oven cavity, and fastening means adjacent the ends of the fulcrum rod for supporting the sensor from the oven walls, a hydraulic cylinder located in the driven rod and connected to the capillary tube for converting variations in the length of the driven rod to variations in hydraulic pressure in the capillary tube.

5. A domestic oven having walls defining an oven cooking cavity, one wall of the cavity including a door for gaining access thereto, heating means for the cavity for supplying heat for cooking food placed therein, a hydraulic thermostatic control system for governing the oven heating means, said control system including a temperature sensor and an adjustable thermostat, and a fluid-filled capillary tube connecting the sensor to the thermostat, the sensor being in the form of an open framework having three spaced substantially parallel rods, a temperature sensing rod, a central fulcrum rod, and a driven rod, the adjacent ends of the rod joined together by a rocker arm that is integral therewith, the sensing rod being a direct expansion member that is positioned within the oven cavity and exposed to relatively high temperatures, the rocker arms extending through a wall of the oven cavity to dispose both the fulcrum rod and driven rod outside of the oven cavity in the same ambient conditions of relatively low temperatures, and fastening means adjacent the ends of the fulcrum rod for supporting the sensor from the oven walls, a hydraulic slave piston assembly interposed in the driven rod, one end of the capillary tube being connected to the slave piston assembly, whereby variations in the temperature within the oven cavity will cause the length of the sensing rod to vary as a function thereof, the move ment in the sensing rod causing the rocker arms to pivot about the fulcrum rod and cause inverse movement in the driven rod and result in functional variation in hydraulic pressure in the slave piston assembly and capillary tube.

References Cited by the Examiner UNITED STATES PATENTS 1,759,222 5/1930 Claus 236-15 2,565,350 8/1951 Burns et al 23615 FOREIGN PATENTS 622,536 11/ 1935 Germany.

ALDEN D. STEWART, Primary Examiner, 

1. A HYDRAULIC THERMOSTATIC SYSTEM FOR CONTROLLING THE HEATING MEANS OF A DOMESTIC OVEN COMPRISING A TEMPERATURE SENSOR AND A HYDRAULIC TEMPERATURE RESPONDER THAT ARE JOINED TOGETHER BY A FLUID-FILLED CAPILLARY TUBE, THE SENSOR COMPRISING A RECTANGULAR FRAME WITH A SENSING TUBE A LOW THERMAL MASS FORMING ONE SIDE, A DRIVEN TUBE FORMING THE OPPOSITE SIDE, AND WHERE THE TWO REMAINING SIDES ARE ROCKER ARMS CONNECTED THE SENSING TUBE WITH THE DRIVEN TUBE, AND A FULCRUM ROD ADJACENT THE CENTER OF THE FRAME AND INTEGRAL AT EACH END WITH THE ADJACENT ROCKER ARM. AND A TRANSDUCER COOPERATING WITH THE DRIVEN TUBE AND CONNECTED TO THE CAPILLARY TUBE SO AS TO CONVERT VARIATIONS IN THE LENGTH OF THE DRIVEN TUBLE TO VARIATIONS IN THE FLUID PRESSURE IN THE CAPILLARY TUBE, THE SENSING TUBE BEING ADAPTED TO BE POSITIONED WITHIN AN OVER CAVITY WHILE BOTH THE FULCRUM ROD AND THE DRIVEN TUBE ARE ADAPTED TO BE SHIELDED FROM THE OVEN TEMPERATURE AND LOCATED IN THE SAME AMBIENT CONDITIONS TO RENDER THAN AMBIENT TEMPERATURE COMPENSATED SO THAT THE NET EFFECT IS THAT ONLY THE SENSOR TUBE LENGTH IS MONITORED BY THE DRIVEN TUBE. 